Good Heavens, No

The guillotine is not medieval. While there were some predecessor devices that were, the guillotine came to be during a debate of the parliament that produced the French Revolution. Its association with that revolution, and especially its frequent use during the Terror, made it a symbol of the Age of Reason and the Enlightenment.

As a member of the assembly Guillotin mainly directed his attention towards medical reform, and it was on 10 October 1789, during a debate on capital punishment, that he proposed that "the criminal shall be decapitated; this will be done solely by means of a simple mechanism." The "mechanism" was defined as "a machine that beheads painlessly". His proposal appeared in the Royalist periodical, Les Actes des Apôtres.

At that time, beheading in France was typically done by axe or sword, which did not always cause immediate death. Additionally, beheading was reserved for the nobility, while commoners were typically hanged. Dr. Guillotin assumed that if a fair system was established where the only method of capital punishment was death by mechanical decapitation, then the public would feel far more appreciative of their rights.

Despite this proposal, Guillotin was opposed to the death penalty and hoped that a more humane and less painful method of execution would be the first step toward a total abolition of the death penalty. He also hoped that fewer families and children would witness executions, and vowed to make them more private and individualized. It was also his belief that a standard death penalty by decapitation would prevent the cruel and unjust system of the day.

So it was all about reforming the law to eliminate distinctions between classes, about bringing reason and science to bear on social problems, and about reducing the pain and cruelty of the death penalty (with an eye towards its eventual abolition, as France did in 1981). It would be ironically appropriate for the Enlightenment's foremost weapon to be brought to bear against ISIS.

It was also his belief that a standard death penalty by decapitation would prevent the cruel and unjust system of the day.

I think given the number of executions in the Reign of Terror, what he did made it easier to do so because:

It distributed responsibility from the executioner and the judge, to some machine built by unseen hands. Easier to justify, easier to maintain, and one doesn't need to muscle carve one's way through bone and neck by hiring thousands of executioners.

It made execution less painful on the public awareness, which dramatically increases people's tolerance to it, much like pro war propaganda vs anti war propaganda.

Giving him the benefit of the doubt, he had some unintended consequences, rather than intended consequences.

I don't know about the Middle Ages, but during the frantic religious persecutions of the Reformation, if you were unlucky you were burned to death. If they wanted to cut you some slack, you might be strangled before the flames hit; sometimes friends were allowed to supply you with bags of gunpowder to wear so that the flames would set off an explosion that would dispatch you quickly. If you were really lucky you would be beheaded--especially if you had a competent headsman.

It's an irony of sorts that most of the really horrifying punishments we associate with the term "medieval" are really from the Renaissance, Reformation or Enlightenment. Even in the Middle Ages, the rulers characteristically famous for horrible punishments -- Edward I of England, for example -- were well-educated modernizers who got the ideas from studying the history of Rome. The Romans were real innovators, and so the recovery of new works of classical civilization that inspired the early scientific revolutions also inspired really thoughtful tortures and edifying, exemplary ways of putting your opponents to death.